Hydrocracking of coal in molten zinc iodide

ABSTRACT

COAL IS CONTINUOUSLY HYDROCRACKED IN SUSPENSION IN A CONTINUOUS-PHASE MOLTEN SALT PREDOMINATING IN ZINC IODIDE, AT A TEMPERATURE OF FROM ABOUT 300* C. TO AVOUT 500*C. AND UNDER A PRESSURE OF FROM ABOUT 200 P.S.I.G. TO ABOUT 3000 P.S.I.G. THE MOLTEN ZINC IODIDE CONTAINS A SUBSTANTIAL PROPORTION OF ALKALI METAL IODIDE AS A MELTING POINT DEPRESENT, SUFFICIENT TO LOWER THE MELTING POINT FROM ABOUT 446* C., THE NORMAL MELTING POINT OF ZINC IODIDE, TO SUBSTANTIALLY BELOW 350* C. THE MOLTEN ZINC IODIDE CATALYST ALSO CONTAINS AMMONIA, AMMONIUM IODIDE AND WATER, IN SMALL PROPORTIONS, RESULTING FROM HYDROCRACKING THE COAL, ALL OF WHICH ARE ALSO MELTING POINT DEPRESENTS FOR ZINC IODIDE. THE SLURRY OF COAL IN THE MOLTEN CATALYST SYSTEM IS PREPARED BY FIRST SLURRYING GROUP COAL IN AT LEAST 12 TO ABOUT 25-FOLD PROPORTIONS BY WEIGHT MOLTEN IODIDE SALT MIXTURE PREDOMINATING IN ZINC IODIDE AND CONTAINING ALKALI METAL IODIDE. THE RESULTING SLURRY OF COAL IN THE MOLTEN SALT MIXTURE IS THEN CONCENTRATED BY SEPARATING A PORTION, AT LEAST ONE-THIRD, OF THE MOLTEN SALT MIXTURE, TO PROVIDE A STILL PUMPABLE SLURRY OF COAL IN MOLTEN SALT, WHICH IS THE CHARGE TO THE HYDROCRACKING ZONE. THE SEPARATED EXCESS MOLTEN SALT IS RECYCLED TO THE PRIMARY SLURRY ING OPERATION TO PROVIDE A PORTION OF THE MOLTEN SALT FOR SLURRYING THE COAL. THE MOLTEN SALT MIXTURE WITHDRAWN FROM THE HYDROCRACKING OPERATION IS SEPARATED FROM VOLATILE AND NORMALLY LIQUID PRODUCTS OF THE REACTION, AND A MAJOR PROPORTION THEREOF IS RECYCLED TO THE PRIMARY SLURRYING STEP. A MINOR PROPORTION OF THE MOLTEN SALT MIXTURE IS EXTRACTED WITH AN AROMATIC SOLVENT TO REMOVE RESULTING TRA-LIKE MATERIAL AND THEN FILTERED TO REMOVE SOLIDS, AFTER WHICH THE SEPARATED MOLTEN SALT IS RECYCLED TO THE PRIMARY SLURRYING OPERATION.

R. A. LOTH 3,790,468

HYDROCHACKING' OF COAL IN MOLTEN lZINC IODIDE Feb. 5, 1974 l llll 1 @UE, -,.H

2 cm1., L. mr? ,www um; @N /JNU n A om n E m HSN@ S NN United StatesPatent O 3,790,468 HYDROCRACKING F COAL IN MOLTEN ZINC IODIDE Rene A.Loth, Spring, Tex., assigner to Shell Oil Company Filed Mar. 16, 1973,Ser. No. 342,112

Int. Cl. Cg 1/06' U.S. Cl. 208-10 9 Claims ABSTRACT OF THE DISCLOSURECoal is continuously hydrocracked in suspension in a continuous-phasemolten salt predominating in zinc iodide, at a temperature of from about300 C. to about 500 C. and under a pressure of from about 200 p.s.i.g.to about 3000 p.s.i.g. The molten zinc iodide contains a substantialproportion of alkali metal iodide as a melting point depressant,suflicient to lower the melting point from about 446 C., the normalmelting point of zinc iodide, to substantially below 350 C. The moltenzinc iodide catalyst also contains ammonia, ammonium iodide and Water,in small proportions, resulting from hydrocracking the coal, all ofwhich are also melting point depressants for zinc iodide. The slurry ofcoal in the molten catalyst system is prepared by first slurrying groundcoal in at least 12 to about -fold proportions by weight molten iodidesalt mixture predominating in zinc iodide and containing alkali metaliodide. The resulting slurry of coal in the molten salt mixture is thenconcentrated by separating a portion, at least one-third, of the moltensalt mixture, to provide a still pumpable slurry of coal in molten salt,which is the charge to the hydrocracking zone. The separated excessmolten salt is recycled to the primary slurrying operation to provide aportion of the molten salt for slurrying the coal. The molten saltmixture Withdrawn from the hydroeracking operation is separated fromvolatile and normally liquid products of the reaction, and a majorproportion thereof is recycled to the primary slurrying step. A minorproportion of the molten salt mixture is extracted with an aromaticsolvent to remove resulting tar-like material and then iiltered toremove solids, after which the separated molten salt is recycled to theprimary slurrying operation.

BACKGROUND OF THE INVENTION Field of the invention This inventionrelates to the hydrocracking of coal in a slurry of coal in a moltencatalyst system comprising predominately zinc iodide.

Description of prior art An extensive amount of research and developmentwork has been done by a number of Workers on the conversion of coal toliquid hydrocarbon products. Much work has been carried out on thehydrocracking of coal in the presence of a continuous phase of moltenzinc chloride as catalyst by workers at Consolidation Coal Company,under the sponsorship of the Oce of Coal Research, U.S. Department ofthe Interior. Many publications have been based upon this work,including a number of patents, e.g., US. Nos. 3,355,376; 3,371,049;3,594,329; 3,625,861 and British Pat. 1,095,851. Others have also beenactive in this field. U.S. Pat. 3,543,665 is directed to a similarprocess involving the use of various molten metal halides, particularlycertain tri-halides of antimony, bismuth, and arsenic. Still further,U.S. Pats. 3,657,108 and 3,685,962 are directed to the regeneration ofmetal halide-ammonium halide complexes which are formed in the use ofcertain molten metal halides, including zinc iodide, in thehydrocracking of coal. It has also 3,790,468 Patented Feb. 5, 1974 beendisclosed in U.S. 3,667,932, in the use of molten zinc halides in thehydrocracking of heavy oil fractions, that various advantages areobtained by the addition of various melting point depressants, such asthe corresponding alkali metal halides to the molten zinc halide system.

In spite of the extensive elforts which have gone into attempts todevelop practical catalytic processes for the conversion of coal touseful liquid hydrocarbon products, there still is no large-scalecommercial application of any of these processes-no doubt due in largemeasure to the multiplicity of technical and economic problems whichremain to be solved.

SUMMARY OF THE INVENTION This invention provides a continuous process ofhydrocracking coal in a slurry of coal in a multi-proportion of a moltenmass predominating in zinc iodide by contacting the slurry with hydrogenat a pressure of about 200- 3000 p.s.i.g. and at a temperature of fromabout 300 C. to about 500 C., in which the following combination ofsteps is involved:

l) vContinuously slurrying the coal in particulate form to a pu-mpableslurry in a circulating stream of an at least l2-fold weight proportionof a molten salt mixture, consisting essentially of zinc and alkalimetal iodide under substantially non-cracking conditions and at atemperature substantially below the normal melting point of zinc iodide;the amount of alkali metal iodide being suflicient to give, with thezinc iodide present, a two-component mixture thereof having a rstsolidication point (melting point) below 350 C.;

(2) Separating at least about one-third of the molten salt mixture fromthe slurry and producing a concentrated, still pumpable slurry therefromhaving a higher coal-solids content e.g., a molten salt to coal weightratio of from about 7 to 12, and recycling the remaining portion of themolten salt mixture, depleted in coal, to the slurrying step;

(3) Subjecting the concentrated slurry to hydrocracking at a pressure ofat least about 200 p.s.i.g., e.g., about 200-3000 p.s.i.g., and atemperature of about 300 to about 500 C. in the presence of hydrogen;

(4) Recovering the resulting hydrocracked products from the molten saltmixture and coal residue, including tar and ash;

(5) Separating and recycling a major portion of the molten salt mixtureand suspended coal residue to the coal slurrying step; and

(6) Recovering a purified molten salt mixture from the remainder of themolten salt mixture and coal residue and recycling the recovered moltensalt material to the coal slurrying step.

As previously discussed, the utility of molten zine iodide as a mediumfor the hydroconversion of coal is Well known. In such processes coalmay be directly introduced as such with hydrogen into the hydrocrackingzone containing the molten salt mixture. Alternatively, the coal may beiirst slurried in the molten salt mixture and then introduced into thehydrocracking zone. The present invention concerns an improvedhydrocracking process in which the 'weight ratio of molten salt to coalin the slurry employed to transport the coal to the reactor, and theweight ratio of coal to molten salt mixture in the reactor per se, arecontrolled in such a manner as to achieve a high degree of efficiencyand to avoid unnecessary material handling, heating and cooling. Inaccordance with the invention, ground coal (e.g., 60-300 mesh) isintimately mixed with at least about a l2-fold, preferably 15 to 25fold,proportion by weight of a molten zinc iodide-containing salt mixturethereby forming a pumpable slurry which is transported to the reactionzone under substantially non-cracking conditions, i.e., under conditionsof low temperature, e.g., 250-300 C., so that undesirable thermalconversion of the coal into tar and other heavy products is avoided.Before entering the reactor, at least about one-third of the slurry,preferably one-third to two-thirds, is separated from the balance of theslurry, and the coal therein concentrated to produce a still pumpableslurry containing no more than about a 7 to 12fold by weight proportionof the molten salt mixture relative to the slurried coal. Thisconcentrated slurry enriched in coal is fed to the reactor while theremaining portion of the slurry, containing a lesser proportion of coal,is recycled to the coal slurrying step. It has been found thatconcentration of the slurry can be very effectively accomplished by useof a series of liquid cyclones (hydroclones) because of the differencein specie gravity of the molten salt and the coal in the slurry.Centrifuges or comparable separators can also be employed to increasethe concentration of coal in the slurry.

In further accordance with the invention, hydrocracking is effected at apressure of about 20G-3000 p.s.i.g., preferably 1000 to 3000 p.s.i.g.,and a temperature of about 300 to 500 C., preferably 400 to 450 C. Thehydrocracked products are separated from the molten salt mixture andrecovered. A major portion of molten salt mixture containing minoramounts of coal residue and other impurities is recycled from thereaction zone to the slurrying step and utilizedfor slurrying furtheramounts of coal. The remainder of the salt mixture is preferablysubjected to one or more purification steps as hereinafter discussedbefore recycle to the slurrying step. The invention will now be furtherdescribed by reference to the accompanying drawing.

THE DRAWING The sole figure of the accompanying drawing is a schematiciiow diagram illustrating a preferred embodiment of the invention.

PREFERRED EMBODIMENT OF THE INVENTION Referring to the drawing,previously ground and dried coal is supplied by line 11 to a coal hopper12 from which the coal is delivered by line 14 to a slurry mixer 15,provided with a stirrer operated by motor 16. The coal is intimatelymixed and slurried with molten salt supplied by line 17. Molten salt forstart-up of the operation, and make-up salt after the process is incontinuous operation is supplied through lines 19, 20, and 17. Themolten salt is predominately zinc iodide containing a sufficientproportion of alkali metal iodide, together with some ammonium iodideresulting from the subsequent reaction of the coal and to some extent asmall proportion of Water, to insure that the molten salt mixture issuiiiciently fluid at non-cracking conditions for the coal, for example,at about 250300 C. (preferably about 250 C.).

It may be determined that a mixture of zinc iodide and lithium iodidecontaining about 33% weight lithium iodide has a melting point of about250 C.; a mixture of zinc iodide and sodium iodide containing about 13%weight sodium iodide is molten at 250 C.; a mixture of zinc iodide andpotassium iodide containing about 9% weight potassium iodide has amelting point of about 250 C.; and water to the extent of about 6% byweight in zinc iodide lowers the melting point of the zinc iodide toabout 200 C. At a weight ratio of molten salt to coal of at least 12 toabout 25, the molten salt having the required low melting temperature, areadily pumpable slurry is obtained. The weight ratio of molten salt tocoal in the slurry mixture is preferably about 15 tofabout 25, and morepreferably about 20. This slurry is transferred through line 24, by acirculation pump 2S via line 26 to a series of liquid cycloneseparators, represented by a single cyclone 27, wherein the slurry isseparated into an overhead fraction (withdrawn through line 30) which ismore concentrated in coal and a bottom fraction containing the moredense excess molten salt which is withdrawn through line 29 and returnedby line 17 to slurry mixer 15. The slurry withdrawn from the slurrymixer has a typical specific gravity of about 2.6 at about 250 C.,whereas that in line 30 discharging into slurry surge |vessel 31 andeventually withdrawn therefrom as the reactor charge has a typicalspecific gravity of about 2.14 at 250 C. Removal of a portion of themolten salt, having a higher density than the coal, results in the moreconcentrated slurry having a lower density.

The thus prepared concentrated slurry is maintained as such in slurrysurge vessel 31, provided with a stirrer powdered |by motor 32. 'Iheslurry is withdrawn therefrom through line 34 and pumped by reactorcharge pump 35, whereby the pressure of the slurry stream is raised toabout Z500-2600 p.s.i.g., through line 36 to the bottom of the reactor37. Hydrogen is supplied to the reactor by line 39 (for start-uppurposes the hydrogen is passed through heater 40). The reaction mixtureis maintained in the reactor at a temperature of about 300-500 C.,preferably about 400-450 C., and typically at about 420 C. Theexothermic heat of the hydrocracking process is suicient to maintain thedesired reaction temperature. Reactor 37 is maintained partially lledwith the slurry and resulting liquid products, with a gas phase in theupper portion of the reactor. Vapors in the upper portion of the reactorare withdrawn through a suitably valved and controlled line 41, andsuitably processed for separation and recovery of the componentsthereof.

The ilow rate of the slurry into the reactor and the withdrawal ofliquid through line 42, taking into consideration the relative size ofthe reactor, are selected to provide a residence time in the reactor offrom about 15 to about 30 minutes. The temperature in the reactor may besuch that the addition of very little, if any, melting point depressantis required to maintain the zinc iodide in the molten state therein.This may be adequately provided in the reactor by ammonium iodide Whchresults from conversion of nitrogen-containing components of the coal,and water which results from conversion of combined oxygen in the coal,to the extent that they remain in the zinc iodide under the conditionsin the reactor (a substantial amount of each does remaindissolved-functioning as very effective melting point depressants forthe zinc iodide).

The liquid reaction mixture of molten salt, liquid reaction products andsuspended coal residue, including heavy tar and ash, is withdrawnthrough line 42 and cooled in heat exchangers 44 and 45, then passedthrough a suitable expansion device, as indicated by slurry expander 46,and passed to a flash vessel 47 at a pressure of about 40-60 p.s.i.g.,the temperature having been reduced to about 250 C. The ashed andvaporized products are removed by a suitably valved and controlled line49, and subsequently processed for separation and recovery of theproducts thereof, as will be understood from the prior art.

As representative of the conversions which can be effected in theprocess, the hydrocracking of coal in a zinc iodide-potassium iodidesalt mixture containing about 9% by Weight potassium iodide, at a Weightratio of salt to coal of about 8, at 420 C. and a pressure of 2000p.s.i.g., for a time of about 30 minutes, gave rise to the followingproducts in grams per grams of moisture and ashfree (MAF) coal: 3.5grams of C1-C2 hydrocarbons; 27.2 grams of C.,-216 C. B.P. hydrocarbons,and 27.7 grams of a 216 C.-400 C. B.P. hydrocarbon fraction.

The molten salt mixture in ash vessel 47, containing a small portion ofwhat might be called coal residue, including tar and ash, is dividedinto two streams, one withdrawn through line 60 and the other throughline 51. The major portion, about 70-90% by weight of the total(typically about 80%), is withdrawn through line S0 and recycled to theslurry mixer through lines 22 and 17. The remainder of the molten saltmixture is Withdrawn through line S1 and is mixed with a suitablearomatic hydrocarbon solvent from line 52, and thoroughly mixed inextractor-mixer 54 provided with a stirrer powered by a motor 55. Theresulting mixture is passed through line 56 to settler 57, wherein theorganic extract of aromatic solvent containing dissolved tar isseparated and removed through line 59.

The extracted catalyst melt containing suspended solids is transferredby line 60 to a suitable pressure lter 63, wherein the solids areseparated and removed by the line 61 and the liquid, comprising moltensalt, is withdrawn by line 62, stripped as desired in stripper 66 toremove ammonia and water, and pumped by pump 64 through recycle line 65to line 20 and line 17 and thence back to the slurry mixer.

Certain advantages of this invention will appear from a consideration ofcertain factors which are involved in a suitable large-scale operationfrom the conversion of coal to liquid hydrocarbon products suitable tobe used directly as fuel or to be further converted into materials whichare directly useable as such. For example, it has been determined thatfor a coal conversion plant to produce the equivalent of about 100,000barrels per day of liquid hydrocarbon products, which might beconsidered to be comparable to a moderate petroleum refinery unit,something on the order of 22,000 tons per day of coal would need to beprocessed. In order to hydrocrack that amount of coal in a molten zinciodide catalyzed process according to this invention, it would require acirculating stream of molten salt to the reactor of the order of 22million pounds per hour, under the favorable ratio of molten salt tocoal of about to 1. But, in order to provide the initial slurry of thecoal for Suitable handling, the coal would require approximately twiceas much molten salt for the initial slurrying operation at thenon-cracking conditions. Thus, it is clear that it is highlyadvantageous to provide a process which does not require passing all ofthe molten salt originally required to produce the slurry through thehydrocracking reaction zone.

What is claimed is:

1. In a continuous process of hydrocracking coal in a slurry of coal ina major proportion of a molten salt mixture predominating in zinc iodideby contacting the slurry with hydrogen at a pressure of about 200 to3000 p.s.i.g. and at a temperature of from about 300 C. t0 about 500 C.,the improvement which comprises the combined steps of:

(1) continuously slurrying coal in particulate form to a pumpable slurryin a circulating stream of at least a 12-fold proportion of a moltensalt mixture consisting essentially of Zinc iodide and alkali metaliodide under substantially non-cracking conditions and at a temperaturesubstantially below the normal melting point of zinc iodide, and theamount of alkali metal iodide being sucient to give with the zinc iodidepresent a two-component mixture thereof having a irst soliditicationpoint below 350 C.,

(2) separating at least about one-third of the molten salt mixture fromthe slurry and producing a concentrated, still pumpable slurry therefromhaving a molten salt to coal weight ratio of from about 7 to 12, andrecycling the remaining portion of the molten salt mixture, depleted incoal, to the slurrying step,

(3) subjecting the concentrated slurry to hydrocracking at a pressure ofabout 200-3000 p.s.i.g. and at a temperature of about 300 to about 500C. in the presence of hydrogen,

(4) recovering the resulting hydrocracking products from the molten saltmixture and coal residue,

(5) separating and recycling a major portion of the molten salt mixtureand suspended coal residue to the slurrying step, and

(6) recovering a puriied molten salt mixture from the remainder of themolten salt mixture and coal residue and recycling the recovered moltensalt mixture to the coal slurrying step.

2. The process of claim 1 wherein the coal is slurried in step (1) withl5 to 25 parts by weight, based on the coal, of the molten zinciodide-alkali metal iodide mixture.

3. The process of claim 2 wherein from one-third to two-thirds of themolten iodide salt mixture is separated from the slurry to produce theconcentrated slurry which is hydrocracked.

4. The process of claim 3 wherein the concentrated slurry ishydrocracked at a pressure of about 1000-3000 p.s.i.g. and at atemperature about 400 to 450 C.

5. The process of claim 4 wherein the portion of the molten salt mixtureand suspended coal residue separated and recycled to the coal slurryingstep is from about to by weight of the total.

6. The process of claim 1 wherein concentration of the molten saltmixture Separated from the slurrying step (2) is effected with the useof a liquid cyclone separator.

7. The process of claim 1 wherein the purified molten salt mixturerecovered in step (6) is puried by extraction with an aromatichydrocarbon solvent.

8. The process of claim 7 wherein the extracted molten salt mixture isstripped to remove ammonia and water.

9. The process of claim 2 wherein the coal is slurried in about 20 partsby weight of the molten salt in step (1), about one-half of the moltensalt is separated from the slurry in step (2), and is concentrated to amolten salt t0 coal weight ratio of about 10, the concentrated slurry ishydrocracked at about 400-450 C. and a pressure of about Z500-2600p.s.i.g. in step (3), and about 80% of the molten salt mixture isseparated and recycled in step `(5).

References Cited UNITED STATES PATENTS 3,657,108 4/19'72 Kiovsky l208-10 3,355,376 11/1967 Gorin et al. 208-10 PAUL M. COUGHLAN, JR.,Primary Examiner V. OKEEFE, Assistant Examiner

